Terraform Variables

Terraform Variables: Best Practices and Use Cases

This guide covers the different types of variables in **Terraform**, their use cases, and best practices to manage them efficiently.

---

Overview of Terraform Variables

Variables in Terraform allow for the parameterization of configurations, making deployments more flexible and reusable.

Terraform supports three primary types of variables:

• Input Variables (var) – Define dynamic values for Terraform modules.
• Environment Variables (TF_VAR_name) – Pass values externally without modifying files.
• Output Variables (output) – Display key information after deployment.

---

Defining Input Variables

Input variables make Terraform configurations more dynamic and reusable.

Example of Variable Definition

Create a file named variables.tf:

variable "vpc_cidr" {
  description = "CIDR block for the VPC"
  type        = string
  default     = "10.0.0.0/16"
}

Using Variables in Terraform Code

Use the defined variable in a Terraform resource:

resource "aws_vpc" "main" {
  cidr_block = var.vpc_cidr
}

Passing Variables

Variables can be passed in multiple ways:

• Using a .tfvars file: Create terraform.tfvars with the following content:

vpc_cidr = "10.1.0.0/16"

Run Terraform with:

terraform apply -var-file=terraform.tfvars

• Passing via CLI:

terraform apply -var="vpc_cidr=10.2.0.0/16"

• Using Environment Variables:

export TF_VAR_vpc_cidr="10.3.0.0/16"
terraform apply

---

Variable Types and Best Practices

Terraform supports different data types for variables:

String

variable "region" {
  type    = string
  default = "us-east-1"
}

Number

variable "instance_count" {
  type    = number
  default = 2
}

Boolean

variable "enable_logging" {
  type    = bool
  default = true
}

List

variable "azs" {
  type    = list(string)
  default = ["us-east-1a", "us-east-1b"]
}

Map

variable "instance_type_map" {
  type = map(string)
  default = {
    dev  = "t2.micro"
    prod = "t3.medium"
  }
}

Usage:

instance_type = var.instance_type_map[terraform.workspace]

Object

variable "vpc_config" {
  type = object({
    cidr_block = string
    enable_dns_support = bool
  })
  default = {
    cidr_block = "10.0.0.0/16"
    enable_dns_support = true
  }
}

---

Output Variables

Output variables provide visibility into infrastructure values after deployment.

Example of an Output Variable

output "vpc_id" {
  value       = aws_vpc.main.id
  description = "The ID of the created VPC"
}

Retrieve outputs after running Terraform:

terraform output vpc_id

---

Best Practices for Terraform Variables

• Use Type Constraints – Define variable types explicitly for validation.
• Separate Variables into Files – Organize variables.tf and terraform.tfvars separately.
• Use Default Values Sparingly – Ensure flexibility by not over-relying on defaults.
• Use Sensitive Variables for Secrets – Mark sensitive data to prevent it from being exposed in logs:

variable "db_password" {
  type      = string
  sensitive = true
}

• Utilize Workspace-Specific Variables – Adapt values based on workspaces (e.g., dev, prod).
• Secure State Files – Store state files securely in S3 with encryption and DynamoDB state locking.

---

This guide ensures secure, scalable, and efficient usage of Terraform variables to optimize infrastructure as code (IaC) deployments!